1. Field of the Invention
The invention relates to a hydrogen-permeable membrane and a manufacturing method thereof.
2. Description of Related Art
A fuel cell system includes a fuel cell, a fuel gas supplying portion which supplies a fuel gas containing a hydrogen gas to the fuel cell, and an oxidizing gas supplying portion which supplies an oxidizing gas containing an oxygen gas to the fuel cell. There are methods of supplying the fuel gas to the fuel cell; a method of directly supplying a stored hydrogen gas; and a method of supplying a hydrogen gas by producing the hydrogen gas from a hydrocarbon compound such as methanol. In the case where the latter method is adopted, the fuel gas supplying portion normally includes a reforming portion which generates a mixed gas (a reformed gas) containing the hydrogen gas from the hydrocarbon compound, and a hydrogen separating portion which separates the hydrogen gas from the reformed gas.
A hydrogen-permeable membrane for making the hydrogen selectively permeate therethrough is provided to the hydrogen separating portion. The reformed gas containing the hydrogen gas is supplied to one surface of the hydrogen-permeable membrane, and the hydrogen gas is extracted from the other surface.
Japanese Patent Laid-Open Publication No. 11-276866 discloses a hydrogen-permeable membrane of a self-supporting membrane type in which Pd (palladium) coating layers are formed on both surfaces of a V (vanadium) base layer. However, when the hydrogen-permeable membrane of this type is used, sufficient hydrogen permeability cannot be obtained.